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Sodium Dithionite Substitute for Waller's Solution

Posted by Franklin Roberts  
Franklin Roberts
Sodium Dithionite Substitute for Waller's Solution
January 29, 2005 06:45PM
If you live in a region where sodium dithionite is restricted or unavailable, you might give this a try. An easily-available substitute for sodium dithionite is sodium metabisulfite (NaMBS). When sodium dithionate does its thing in Wallers solution, it does so by reducing barely-soluble Fe+++ (O, OH) to Fe++ (OH)2 which is water soluble and easily chelated by citric acid. One of the Na dithionite's two identical sulfur atoms scavenges the loose oxygen, oxidizing Na dithionite to Na metabisulfite.

Because Na Dithionite has two identical sulfur atoms, it can undergo two redox reactions. The second sulfur atom donates its available pair of electrons to another molecule of ferric oxy-hydroxide and the process repeats. The NaMBS oxidizes a second time to sodium dithionate (-ate, not -ite), and it is now completely oxidized.

The chemical formula for the two-stage reaction looks something like this:

1. Na-O-SO-SO-O-Na + Fe+++(O,OH) --> Na-O-SO2-SO-O-Na (NaMBS) + Fe++(OH)2
2. Na-SO2-SO-O-Na + Fe+++(O,OH) --> Na -O-SO2-SO2-O-Na + Fe++(OH)2

As you can see, making up Waller's solution with NaMBS instead of Na dithionite would work since it's an intermediate product of the reaction anyway. The only downside to using it is that you must use two molar equivalents of NaMBS versus one of the dithionite to achieve the same results. According to my Merck Index, Na dithionite has a molecular weight of 174.11 g/mole and NaMBS weighs in at 190.11 g/mole. (Notice that the metabisulfite salt weighs exactly 16 g/mole more than the dithionite, the weight of the added mole of oxygen from the first redox reaction.) In order to whip up a batch of Waller's solution with NaMBS, you will have to use 2.18 grams of NaMBS for every gram of Na dithionite called for in the recipe. It would probably be a good idea to add an extra 20% of distilled water to the formula to offset the increased tonicity of the solution resulting from the extra dissolved NaMBS.

Sodium metabisulfite should be a lot easier to buy than sodium dithionite, and it doesn't have that rotten egg smell either, although it does release sulfur dioxide if mixed with acids. (Just be sure to add the NaMBS to the citrate/bicarbonate buffer solution AFTER the bicarb has been added to prevent this.) Na MBS is used as a reducing agent for precipitating pure gold from aqua regia solutions and as a preservative in food and wine because its affinity for oxygen retards spoilage. In fact, those sulfite warning labels on wine bottles specifically refer to NaMBS. You should be able to buy it from any chemical supply or shop that caters to winemakers. You can also get it for USD $2.00/lb online at [www.allseasonsnashville.com] It is sometimes referred to by its old name, sodium pyrosulfite. It can also be found on eBay. Just remember to seal the opened container or it will oxidize, just like Na dithionite will.

Franklin Roberts
Austin, Texas
Lloyd L
Re: Sodium Dithionite Substitute for Waller's Solution
February 06, 2005 10:42AM
Thanks for that Franklin.
I've been impressed with the effect that sodium dithionite solution has had on the few specimens on which I've so far tried it.
In the UK, sodium dithionite is quite difficult to procure, so if your recipe is as effective, or nearly as, then this is very useful information.
Thanks again,
Lloyd
Matthew Neuzil
Re: Sodium Dithionite Substitute for Waller's Solution
February 14, 2005 03:45PM
sodium dilitinide is that the same as SUPER IRON OUT ???
Matt, from an MSDS for Super Iron Out:
Sodium Metabisulfite 20-65%
Sodium Hydrosulfite 20-65%

(I wonder why the great variation in percentage?)
matthew neuzil
Re: Sodium Dithionite Substitute for Waller's Solution
February 14, 2005 08:32PM
meta i would assume means it is hydrated like metatorbornite etc. Idk how it would become hydrated except after being opened.
Franklin Roberts
Re: Sodium Dithionite Substitute for Waller's Solution
February 15, 2005 11:38PM
In this case, the prefix "meta" which is Greek for "after" refers to the fact that the metabisulfite is the species that comes after sodium bisulfite (dithionite) in the chain of oxidation products going from sodium dithionite -> sodium metabisulfite -> sodium dithionate. These three compounds are also known as sodium hydrosulfite, sodium pyrosulfite and sodium bisulfate, respectively. Pretty confusing, isn't it? The reason that super iron-out lists a wide range of percentages for the two ingredients isn't because they don't want you to know how much of each is in their product, it's because they don't know themselves. The actual ratio is a moving target. Remember, pure sodium dithionite is a potent reducing agent capable of snatching two atoms of oxygen from anywhere it can get it, from the air and even from humidity. As soon as it snatches the first oxygen, it becomes sodium metabisulfite and can only grab one more before becoming the fully-oxidized sodium dithionate, which is useless as an iron reducing agent, but great for lowering the pH in your swimming pool. Products such as super iron-out usually are made from industrial grade chemicals that contain a lot more impurities than the reagent or high-purity grades. This bulk grade is sometimes called "product of commerce". The reason for using this feedstock is that the industrial grade chemicals sell for a few dollars a ton, while the pure stuff can cost a few dollars a pound. If all you want to do is remove iron stains from your driveway (or your minerals) industrial grade will work just fine. The feedstock used to make super iron-out probably started out as a moderately pure sodium dithionite (hydrosulfite), but during manufacture and storage, it gradually absorbed oxygen from the air and some of it oxidized, becoming sodium metabisulfite (pyrosulfite). Since the pyrosulfite is still a great reducing agent, it's ok to leave it in the mix, but it's nearly impossible to get an accurate estimate on its proportion. As time goes by, more of the dithionate will transform into the metabisulfite and then to the dithionate. Eventually, the entire batch will become sodium dithionate and it's days as a stain remover are over. That's why it's so important to keep the container sealed against the air after you open it.

Franklin Roberts
Austin, Texas
andy christy
Re: Sodium Dithionite Substitute for Waller's Solution
April 15, 2005 02:26AM
Franklin wrote (Feb 15, 23:38):
"In this case, the prefix "meta" which is Greek for "after" refers to the fact that the metabisulfite is the species that comes after sodium bisulfite (dithionite) in the chain of oxidation products going from sodium dithionite -> sodium metabisulfite -> sodium dithionate. "

Unfortunately, it does not. This usage of "meta" is similar to that in "metasilicate" for silicates with an [SiO3]2- anion instead of "orthosilicate" for [SiO4]2- stoichiometry. In that case, the hypothetical meta acid H2SiO3 is produced by removing H2O from the ortho acid H4SiO4. In the case of metabisulfite, one H2O is removed from two molecules of the hypthetical sulfurous acid H2SO3 to give equally hypothetical H2S2O5, of which NaMBS is the sodium salt.

Matthew Neuzil (Feb 14, 20:32):
"meta i would assume means it is hydrated like metatorbornite etc. "

No. The "meta" in "metatorbernite" implies LESS structural water than in "torbernite", same as above! But "meta" in many minerals is also used to indicate a polymorphic or alteration relationship that is not dehydration, eg metavariscite and variscite, which are polymorphs of the same composition.

Jim (Feb 14, 18:19):
"Matt, from an MSDS for Super Iron Out:
Sodium Metabisulfite 20-65%
Sodium Hydrosulfite 20-65%
(I wonder why the great variation in percentage?)"

Because Na hydrosulfite (= Na dithionite) absorbs oxygen readily from the air, to form metabisulfite, and the manufacturers refuse to guarantee precisely how much of it has turned already. They do suggest that the total of the two stays constant at around 85%. I suspect that the other 15% is dithionate, sulfate and adsorbed water. Even lab reagent dithionite is usually sold as about 85% or so rather than 99+%.
avatar Re: Sodium Dithionite Substitute for Waller's Solution
November 17, 2010 09:34AM
Franklin,
I think it time that someone wrote up an article about the use of Waller solution/Sodium dithionite for cleaning "iron stains" off of minerals. I have used some of the information you have give us here on mindat in my article on cleaning quartz (credit given to you of course), but feel that is has now become such a commonly used method of cleaning iron minerals off of minerals that it really should have its own separate article. I could write it up, but I think you probably have more knowledge of its chemistry and perhaps more experience in than I in making it from scratch and its employment on various minerals than I. Would you consider writing such an article? As usual there is no reward other than your name on the article and the recognition that may come with that. I continue to be amazed as how much use some of these articles get. The one I wrote on cleaning quartz has so far generated something over 23K hits.

In your post you say: in the chain of oxidation products going from sodium dithionite ->. What does -&gt, mean? Google gives no meaningful hits.

Rock Currier
Crystals not pistols.
Re: Sodium Dithionite Substitute for Waller's Solution
December 12, 2010 12:54AM
    
Hi Rock,

Sure, I'd be happy to write such an article. Why don't you PM me so we can coordinate our efforts. I'm still recuperating from my accident and won't be returning to work until after the holidays, so now would be a great time to tackle this project.

Frank

PS -> is what a right arrow becomes when posted to this forum. I've noticed that special characters and some punctuation gets mangled the same way. In order to read the chain of oxidation products correctly, just substitute a right arrow wherever you encounter ->
Re: Sodium Dithionite Substitute for Waller's Solution
December 23, 2010 12:01PM
Thanks for the preceding 5 years old discussion. It would be particularly great if you would describe the optimal concentration and also safe preparation of a simple sodium dithionate solution. For example, on the web there's are lots of warnings about possible ignition of this compound during storing in moist conditions, but I never understood how one can safely prepare a water-solution when only a bit of moisture can cause a danger. On the first sight these two statements seem contradictory smiling smiley
Honza Franek
avatar Re: Sodium Dithionite Substitute for Waller's Solution
December 30, 2010 05:36AM
    
"... but I never understood how one can safely prepare a water-solution when only a bit of moisture can cause a danger. On the first sight these two statements seem contradictory"

It's the concentration that makes the difference. The reaction of dithionite with atmospheric oxygen, or with any oxydant in general, is exothermic. In a dilute solution, and with water as the solvent which has a high specific heat capacity, the temperature increase is not substantial. With moisture in a pure dithionite powder, however, the solution will be saturated or at least close to the saturation point, so the heat production per unit volume will be orders of magnitude higher. Since the powder consists of solid particles with ambient air in interstitial spaces, and gases in general have a very low specific heat capacity, considerable temperatures are locally reached fairly easily. Temperature, however, increases the reaction rate, so the process is self-accelerating and the heat production increases exponentially. Above a certain temperature, dithionite starts to decompose even without an oxydant and the mixture explodes.
Re: Sodium Dithionite Substitute for Waller's Solution
January 07, 2011 12:37PM
    
Perhaps if you manage to word together a guide to the Waller method/Na-dithionite it could be added to the mineral cleaning article I've been trying to get off the ground (with little support!).

For those who mightn't know about it: [www.mindat.org]
avatar Re: Sodium Dithionite Substitute for Waller's Solution
January 08, 2011 03:30AM
    
Barry,

A detailed guide on how to remove iron stains with dithionite is essentially contained in Rocks's article about cleaning quartz, which is available somewhere on this site.
E.Abbott
Re: Sodium Dithionite Substitute for Waller's Solution
January 08, 2011 05:28AM
What about this, seems a good guide- Link
avatar Re: Sodium Dithionite Substitute for Waller's Solution
January 08, 2011 07:17AM
    
This article is largely okay. However, I always wonder what some people consider as a buffer - not just an additive for pH adjustment. In fact, at the proposed composition, the buffer capacity will be close to nil. Also, why does a complexing agent (= sequestering agent) have to be used at all, when Fe(OH)2 is that much better soluble than Fe(OH)3 ?

Rock's article addresses the cleaning process in more detail and gives a wealth of practical tips that will help to "customize" it accprding to your personal needs.
avatar Re: Sodium Dithionite Substitute for Waller's Solution
January 08, 2011 11:27AM
That particular article is a link suggested as part of the Cleaning Quartz article refers to.

Rock Currier
Crystals not pistols.
Re: Sodium Dithionite Substitute for Waller's Solution
January 08, 2011 02:02PM
As a chemist and all mineralogist's are branch of this science or art.

A member of the ROM staff told me Waller's soln was verboten caused by unavailability of sodium hydrosulphite, dithionite or sulfoxylate was difficult to obtain.

Since I have seen drums abet small outside the local dyehouse, so this suprised me

It is also used in water treatment Boilers I think and paper mills?

I would be suprised if it wasn't in toilet bowl cleaners esp. in high iron areas. I have used this.
I am more worried about the production of hydrogen sulphide

We used to be able to purchase "chemicals" from the druggist's ie chemist's to you Brit's

PC of big brother has eliminated this source and you have to have a account number from your local chemical supplier with everything but your maiden aunt's name.

Think of Ammonium nitrate except for Oppau it wasn't until 1947 it's explosive properties were recognized Thanks to Haber it is still produced safely in bulk esp. for gardeners

Thedifference between a medicine and a poison is the dose
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